1. Field of the Invention
The present invention relates to an exposure apparatus that is used when manufacturing an electronic device, such as a semiconductor device, a liquid crystal display device, an imaging device (CCD and the like), and a thin film magnetic head, and also relates to a device fabricating method.
2. Description of Related Art
When fabricating an electronic device, such as a semiconductor device and a liquid crystal display device, by a photolithographic process, a projection exposure apparatus is used that projects a pattern image of a mask or a reticle (hereinafter, generically referred to as a reticle), wherein a pattern is formed through a projection optical system onto every projection (shot) region on a substrate, which is coated with a photosensitive material (resist). The circuit of the electronic device is formed by transferring the circuit pattern onto the substrate to be exposed by exposing it with the abovementioned projection exposure apparatus and then performing postprocessing.
The level of integration of integrated circuits, i.e., the fineness of circuit patterns, has been increasing in recent years. Consequently, there is a trend towards shorter wavelengths in the illumination beam for exposure (exposure light) used in projection exposure apparatuses. Namely, short wavelength light sources, such as a KrF excimer laser (248 nm wavelength), are beginning to be used instead of the mercury lamp, which has been the mainstream light source until recently, and exposure apparatuses that use even shorter wavelength ArF excimer lasers (193 nm) are entering the final stages of commercialization. In addition, the development of an exposure apparatus that uses an F2 laser (157 nm) is in progress with an aim toward achieving even higher levels of integration.
Beams that have a wavelength of less than approximately 190 nm belong to the vacuum ultraviolet region, and such beams do not transmit through air. This is because the energy of the beam is absorbed by substances (hereinafter, generically referred to as light absorbing substances), such as oxygen, water and carbon dioxide molecules contained in the air.
In an exposure apparatus that uses exposure light in the vacuum ultraviolet region, light absorbing substances must be reduced in, or eliminated from, the space along the optical path of the exposure light, so as to achieve a sufficient illumination intensity of the exposure light on the substrate to be exposed. Consequently, in an exposure apparatus, the space along the optical path is enclosed by a casing, and a transmissive gas that transmits the exposure light is supplied to the interior of that casing. In this case, if the total length of the optical path is, for example, 1000 mm, then the concentration of the light absorbing substances inside the space along the optical path is, for practical purposes, less than approximately 1 ppm.
Nevertheless, because of the frequent exchanging of the substrate, it is problematic to eliminate the light absorbing substances in the space along the optical path and in the space been the projection optical system and the substrate. For example, to enclose this space with the casing, a constitution is conceivable wherein a large sized casing is installed so that the mechanism for exchanging the substrate can also be enclosed. However, with this constitution, the larger the casing, the greater the quantity of gas that is consumed in supplying the interior of the casing, and the greater the cost burden becomes.
Consequently, with an exposure apparatus, technology to eliminate light absorbing substances from the space along the optical path is being considered, wherein an atmosphere forming mechanism that forms a local gas atmosphere is disposed between the projection optical system and the substrate. With this constitution, the atmosphere forming mechanism is disposed between the projection optical system and the substrate in a state wherein a clearance on the order of several millimeters is provided with respect to the substrate (refer to Japanese Laid-Open Publication No. 2001-210587).
In such an exposure apparatus, the stage, which is used for mounting the substrate, and the projection optical system are each supported by different support platforms. Active vibration eliminating for suppressing vibrations from the floor surface are provided to the support platform on the stage side and the support platform on the projection optical system side, respectively, and the spacing between the stage and the projection optical system is maintained in a prescribed state by the independent driving of these active vibration eliminating apparatuses. If some kind of trouble arises with the active vibration eliminating apparatuses and a movement occurs wherein the projection optical system and the stage mutually approach, then the possibility that a particularly serious problem will occur is small because the amount of that movement is sufficiently small compared with the spacing between the projection optical system and the substrate if the atmosphere forming mechanism is not disposed therebetween. However, if the atmosphere forming mechanism of the type discussed above is disposed between the substrate and the projection optical system, then the clearance between the substrate and the atmosphere forming mechanism unfortunately becomes smaller than the amount of movement discussed above. Furthermore, if some kind of trouble arises with the active vibration eliminating apparatuses, and the projection optical system and the stage mutually approach, then there is a possibility that the stage or the substrate will make contact with the atmosphere forming mechanism. If the stage or the substrate makes contact with the atmosphere forming mechanism in this manner, then the force due to this contact will be transmitted through the atmosphere forming mechanism to the projection optical system, which will adversely alter the imaging performance of the projection optical system.